The preparation of synthetic polymeric membranes for use in reverse osmosis systems is well-known in the art. U.S. Pat. No. 4,277,344, for example, discloses a semipermeable membrane prepared from the reaction of an aromatic polyamine with a polyacyl halide which has been found to be effective in reverse osmosis systems directed at rejecting sodium, magnesium and calcium cations, and chlorine, sulfate and carbonate anions. Because these ions are found in seawater, these membranes are useful for desalinating seawater.
Whater systems containing nitrate salts, such as Ca(NO.sub.3).sub.2 and NH.sub.4 NO.sub.3, however, are not effectively desalinated by the these membranes or other generally available membranes. Because in various areas of the world, ground water supplies have become contaminated with nitrates from fertilizer runoff, stock feeding and other sources, there is a need for a desalination system directed at rejecting nitrate salts. Membranes for use in reverse osmosis systems to be commercially acceptable should be capable of relatively high flux rate and should have resistance to deterioration by hydrolyis and by exposure to high pressure, temperature and dissolved chlorine.
One object of the present invention to provide semipermeable membranes for use in reverse osmosis systems having improved rejection of certain salts, such as nitrates, while maintaining the necessary durability requirements needed for commercial applications.